Yuki Aoki

Oscillation frequency dependence of nonclassical rotation inertia of solid 4He.

The nonclassical rotational inertia fraction of the identical cylindrical solid 4He below 300 mK is studied at 496 and 1173 Hz by a double resonance torsional oscillator. Below 35 mK, the fractions are the same at sufficiently low rim velocities. Above 35 mK, the fraction is greater for the higher than the lower mode. The dissipation peak of the lower mode occurs at a temperature approximately 4 mK lower than that of the higher mode. The drive dependence of the two modes shows that the reduction of the fraction is characterized by critical velocity, not amplitude or acceleration.

New dissipation relaxation phenomenon in oscillating solid (4)He.

We describe the first observations on the time-dependent dissipation when the drive level of a torsional oscillator containing solid (4)He is abruptly changed. The relaxation of dissipation in solid (4)He shows rich dynamical behavior including exponential and logarithmic time-dependent decays, hysteresis, and memory effects.

Search for fourth sound propagation in supersolid He4

A systematic study is carried out to search for fourth sound propagation solid He4 samples below 500mK down to 40mK between 25 and 56bar using the techniques of heat pulse generator and titanium superconducting transition edge bolometer. If solid He4 is endowed with superfluidity below 200mK, as indicated by recent torsional oscillator experiments, theories predict fourth sound propagation in such a supersolid state. If found, fourth sound would provide convincing evidence for superfluidity and a new tool for studying the new phase. The search for a fourth sound-like mode is based on the response of the bolometers to heat pulses traveling through cylindrical samples of solids grown with different crystal qualities. Bolometers with increasing sensitivity are constructed. The heater generator amplitude is reduced to the sensitivity limit to search for any critical velocity effects. The fourth sound velocity is expected to vary as ∝ρs∕ρ. Searches for a signature in the bolometer response with such a characte...